Field of the Invention
The use of bituminous emulsions in road manufacture is becoming more and more important. Air pollution controls limit the use of hot-mix methods in some localities, and these controls are becoming more widespread and more stringent. The use of cold-mix operations, i.e., bituminous emulsions, which can be utilized at ambient conditions is always desirable where practical, since high temperatures required by hot-mix operations are preferably avoided.
When utilizing bituminous emulsions, two criteria must be satisfied. The first of these is that the emulsions themselves must behave satisfactorily, i.e., breakdown, coagulation, viscosity, limitations, etc., must be satisfactory. However, once satisfactory properties of the emulsions themselves have been obtained, the second class of problems arises. This is with regard to the emulsion's asphalt fraction.
The asphalt residuum left after the emulsion has broken and the continuous aqueous phase has evaporated must meet certain criteria. The reheological parameters of asphalt must remain satisfactory throughout the service life of the asphalt surface. Temperature variations encountered over the life of the asphalt are a major determinant of rheological change and any consequent failure of the system. The asphalt residuum must be capable of binding "cover" aggregate utilized almost uniformly in road-surface manufacture. The degree of binder effectiveness is strongly dependent upon its adhesive and cohesive properties. In turn, the magnitude of these adhesive and cohesive properties is greatly influenced by the nature of the asphalt residuum.
At lower temperatures the asphalt residuum binder becomes more elastic and behaves less like a viscous liquid. Under low-temperature conditions, asphalt becomes more susceptible to fracture. When such fracturing occurs at low temperature, the practical effect is that surface vehicles utilizing the road structure cause portions of the aggregate along the fracture lines to become dislodged. The resulting breakdown of the road structure, cracked windshields from flying particles, and the like, are increased.
During the hot summer months, the adhesive properties of an asphalt residuum having a relatively high temperature susceptibility are reduced. The practical effect is the same as in cold weather. The aggregate becomes loose with the consequent increase in flying rock and damage to windshields.
This invention is directed to a method for improving the characteristics of emulsion residuum to reduce temperature susceptibility at both high and low temperatures.